Table 4.6

Table 4.5

SCREWS

Table 4.4

Nominal thread diameter dn, mm	Pitch of thread	S	H	D*	D	с
coarse	fine
	2.0	1.5			27.7	26.5
	2.5	1.5			31.2	29.9	2.5
	2.5	1.5			34.6	33.3	2.5
	2.5	1.5			37.0	35.0	2.5
	3.0	2.0			41.6	39.6

Screws are used where bolts are inconvenient to use. In the case of screws, the threads on the shank are continued to a distance from the head of the screw not exceeding two times the pitch of the thread for diameter up to 25 mm.

A screw is a threaded bar on the first side and a head of different forms on the second. Figure 4.18, a shows а countersunk head screw accoding to State Standard 17475:2008, and figure 4.18, b shows а cheese-head screw accoding to State Standard 1491:2008. The metrical thread of coarse or fine pitches with the tolerance zone 6g and 8g is done on a screw. As a rule, on a screwhead spline under a screwdriver is done. The basic parameters of countersunk head screws and cheese-head screws are resulted in table 4.5.

а) b)

Figure 4.18 – Screws.

The example of denotation of countersunk-head screw, with accuracy A, type 2, threads diameter 12 mm, a coarse pitch, length 45 mm, tolerance zone 8g, the strength class 5,8 without coverage:

Screw A2.M12´45-8g.58 State Standard 17475:2008

Basic parameters of countersunk-head screws are resulted in table 4.5, and cheese-head screws are resulted in table 4.6.

Nominal thread diameter dn, mm	Pitch of thread	D	H	b	h	c	L	Length l0 depending on l*
coarse	fine	l0	l*
	1.75	1.25	21.5			2.5	1.6	22-85		42-85
		1.5					1.6	25-90		47-90
		1.5	28.5			3.5		30-95		55-95
	2.5	1.5	32.5				2.5	35-100		59-100
	2.5	1.5				4.5	2.5	40-110		65-110

Nominal thread diameter dn, mm	Pitch of thread	D	H	b	h	c	r	L	Length l0 depending on l*
coarse	fine	l0	l*
	1.75	1.25				2.5	1.6	0.6	22-85		35-85
		1.5					1.6	0.6	25-90		40-90
		1.5				3.5		0.6	30-95		45-95
	2.5	1.5					2.5	0.6	35-100		50-100
	2.5	1.5				4.5	2.5	0.8	40-110		55-110

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